1. Field of the Invention
The invention relates to television tuners, and more particularly, to a dual mode television tuner for processing both satellite TV signals and digital TV signals.
2. Description of the Prior Art
One of the most significant costs in television manufacturing is the cost of the tuner. Furthermore, with the increasing desire to integrate TV functions into personal computer (PC) systems and other electronic devices, the cost of the tuner needs to be reduced. Additionally, television tuners are no longer just used for processing analog TV signals. Satellite TV and digital TV are both increasing in popularity everyday.
Traditionally, tuners have been comprised of two basic components. The first component performs high frequency to intermediate frequency (RF to IF) conversion. Subsequently, the second component performs IF to baseband conversion. The TV tuner was originally designed for broadcast television reception within a television set, which is essentially a stand-alone unit containing a cathode ray picture tube. So, TV tuners were originally integral parts embedded in a single-purpose device.
Presently, however, state-of-the-art consumer electronic devices use TV tuners that are not a built-in part of a television set. The tuner is a separate element that is connected to a cathode ray picture tube at some point, but the tuner is not an integral part of the monitor. As previously mentioned, TV tuners may be fabricated on circuit boards and then installed in personal computer systems, thereby allowing the PC to function as a television set. These tuners convert a radio frequency television signal into a baseband (or low frequency) video signal, which can then be passed on to other elements in the PC for video processing applications.
FIG. 1 shows a highly integrated television tuner 100 on a single microcircuit as disclosed by U.S. Pat. No. 5,737,035. The television tuner 100 includes an adjustable low noise amplifier 101; a first mixer 102; a first local oscillator 104; a band-pass filter 106; a second mixer 108, which is an image rejection type mixer; a second local oscillator 110; a first intermediate frequency amplifier 112; a second band-pass filter 114; and a variable intermediate frequency amplifier 116. However, as the television tuner 100 requires the use of a special image rejection mixer for the second mixer 108, the cost of the tuner is increased. Additionally, the first local oscillator 104 is used in conjunction with the first mixer 102 to up-convert a particular channel selected from an incoming RF signal. This means the first local oscillator 104 must be a variable frequency local oscillator having a large operating frequency range. Because the phase noise over the operating frequency range of the first local oscillator 104 must meet a specific phase noise requirement, typically 84 dBC/Hz, a plurality of VCOs having smaller frequency ranges, and therefore lower phase noise, must be used. Additionally, the television tuner 100 is not capable of processing satellite TV signals. If a device needs to process both digital TV signals and satellite TV signals, a first television tuner for digital TV signals must be used in addition to a second television tuner for satellite TV signals. This increases the overall cost of the device. Accordingly, a need exists for a television tuner having reduced cost and being capable of processing both digital TV signals and satellite TV signals.